Saad Alshehri

Solvation and reactivity of the low-spin trisdiimine iron(II) complex of the schiff base ligand derived from 2-benzoylpyridine and 3,4-dimethylaniline, [Fe(Me2bsb)3]2+

Abstract The reactivity and solvation of the iron(II) tris complex made from the bidentate ligand obtained by condensing phenyl 2-pyridyl ketone and 3,4-dimethylaniline have been examined in aqueous solution and in aqueous solvent mixtures. Base hydrolysis kinetics measurements upon the complex ion, [Fe(Me 2 bsb) 3 ] 2+ , show an increasing rate of dissociation with increasing co-solvent concentration, due largely to the destabilization of the hydroxide ion. The predicted preference the lipophilic complex would exhibit toward solvents less polar than water is an expectation that is realized when transfer (from water to aqueous solvent mixtures) chemical potential trends are analysed. The latter parameters were obtained from solubility measurements. When corresponding transfer chemical potentials for the transition state are also considered, the factors controlling reactivity patterns are shown; this is described by an initial state—transition state analysis. Base hydrolysis kinetics carried out at high pressures (up to 1 kbar) yield the volumes of activation, Δ V *, which provide a complementary view of solvation. Some measurements with a similar complex, [Fe(Me 2 tsb) 2 ] 2+ , are reported for comparison.

Dissociation kinetics of [Fe(phen)3]2+, [Fe(bipy)3]2+ and [Fe-(4,4′-Me2bipy)3]2+ in the presence of cyanide ion in aqueous solution at pressures up to 1 kilobar

SummaryRate constants for dissociation, in aqueous solution at 25° C, of [Fe(phen)3]2+, [Fe(bipy)3]2+, and [Fe(4,4′-Me2bipy)3]2+ in the presence of cyanide, and of the last-named complex also in the presence of hydroxide, are significantly decreased by the application of pressure (up to 1 kbar). Kinetic measurements were carried out using a high pressure cell of improved design to that used in our earlier investigations. Volumes of activation, ΔV*, are scarcely sensitive to ligand or to attacking nucleophile, being in the range of 10–12 cm3 mol−1. An explanation of these results resides in an associative mechanism, a scheme invoked for similar reactions reported previously.

Salt effects on the kinetics of dissociation of the pentacyano-4-cyanopyridineferrate(II) anion

SummaryThe kinetics of replacement of 4-cyanopyridine (4-CNpy) by CN− in [Fe(CN)5(4-CNpy)]3− have been studied in different concentrations of electrolyte. Plots of ln (k/kw)versus (γ−γw), where the subscript w refers to pure water and γ is the surface tension of the appropriate salt solution, gave a common straight line for all the electrolytes studied. This result seems to confirm theD character of the process studied and permits an estimate of the activation volume to be made from kinetic data.

Structures of bis-ethylmaltolatodichloro-tin(IV) and -titanium(IV) and of trichloro(1-methyl-2-ethyl-3-hydroxy-4H-pyridin-4-onato)aquatin(IV)

Abstract The structures of solvates of the bis-ethylmaltolatodichloro-metal(IV) complexes M(etma)2Cl2, with M=Sn and Ti, and of trichloro(1-methyl-2-ethyl-3-hydroxy-4H-pyridin-4-onato)aquatin(IV), Sn(mepp)Cl3(H2O), have been established by single crystal X-ray diffraction methods. Sn(etma)2Cl2 crystallised with one molecule of dichloromethane, Ti(etma)2Cl2 with one molecule of tetrahydrofuran, and Sn(mepp)Cl3(H2O) with one molecule of acetone, from their respective recrystallisation media. Both ethylmaltol complexes M(etma)2Cl2 are cis-octahedral. The coordination around the tin atom in Sn(mepp)Cl3(H2O) approximates to octahedral, with the three chloride ligands in fac geometry. The tin(IV)–water bond distance in this pyridinone complex is discussed in relation to this distance in other aquatin(IV) complexes. The effects of coordinating tin(IV) on the geometry of the coordinated pyridinone are considered.

Leaving group effects on ligand substitution reactions of pentacyanoferrate(II) complexes: rate constant and activation volume correlations

The kinetics of the reaction of cyanide ions with pentacyanoferrate(II) complexes have been studied spectrophotometrically at pressures of 1 bar and up to 1 kbar, at 298.2 K. An excess of cyanide ions was employed and first-order kinetics were observed both in aqueous solution and in aqueous-mono-ol mixtures. For several pyridine derivative leaving groups, neutral or mono-positively charged, the rate constant variation in aqueous medium is only over one half-order of magnitude, although thiourea and quinoxaline are much more labile, dissociating with rate constants about ten and three hundred times greater than this range, respectively. Very modest changes in rate constant are observed upon addition of 40% methanol, and in a few examples studied, kinetic differences become significant only in cosolvent-rich mixtures. Volumes of activation, Δ V∗, are all positive, for reaction in water, confirming the expected bond extension of the leaving group in a D mechanism. Solvation changes and ligand differences do not wholly explain the variation in Δ V∗ values, or the changes in this parameter found when cosolvents are added. Reasonably good correlations are found for the logarithms of rate constants both with the pKa of the ligand and with Δ V∗. Other potential correlations of the leaving group property and kinetic parameter are discussed.

Solvatochromism and piezochromism of pentacyanoferrate(II) complexes in binary aqueous solvent media

SummaryThe solvatochromic behaviour of a number of pentacyano-ferrates (II), [FeII(CN)5L]n-, is described, for solutions in H2O-alcohol, -Me2CO and -DMSO mixtures. The strong dependence of solvent sensitivity on the nature of the ligand L is particularly fully documented for H2OMeOH mixtures (0–100% MeOH). The piezochromic behaviour of seven pentacyanoferrates(II) has been established, in aqueous solution. The connection between piezochromism and solvatochromism is detailed, and the solvatochromic results discussed in terms of (preferential) solvation.

Volumes of activation for dissociation of pentacyanoferrates(II) through pressure and salt effects on reactivity

SummaryDependences of rate constants on pressure (up to 1 kbar) and on added salt concentration (up to 6.0 mol dm−3 LiNO3, NaNO3, NaCl, Na2SO4 or KNO3) have been established for dissociative substitution of pentacyanoferrates(II), [Fe(CN)5L]3− with L = 4-cyanopyridine, 4,4′-bipyridyl, 4-phenylpyridine and 4-t-butylpyridine. Activation volumes derived directly from pressure effects, and indirectly from salt effects via surface tension dependences and derived surfaces of activation, are reported, compared and discussed.

Solvation of ethylmaltol and of its iron(III) complex

SummarySolubilities of tris(ethylmaltolato)iron(III) (ethylmaltol = 3-hydroxy-2-ethyl-4-pyrone) were measured in MeOH-H2O, t-BuOH-H2O and diol-H2O mixtures, and in several primary alcohols. Solvation of the ethylmaltol ligand and of two 4-pyridinone analogues has been investigated through solubility measurements in MeOH- H2O and in t-BuOH-H2O mixtures, and in a series of primary alcohols. The solvation characteristics of these compounds are compared with those of the parent maltol, its iron(III) complex and a number of other nonelectrolytes.

Activation volumes for peroxodisulphate oxidation of cobalt(III), iron(II) and nickel(II) complexes

SummaryDependences of rate constants on pressure (in aqueous solution up to 1.25 kbar) are reported for peroxodisulphate oxidation of hexacyanoferrate(II), tris(2,2′-bipyridyl)iron(II), tris(1,10-phenanthroline)iron(II), bis(1,4,7-triazacyclononane)nickel(II) and bis(1,2-ethanediamine)cysteinatocobalt(III) and its thioglycollato-analogue, and for periodate oxidation of the two last-named complexes. Derived activation volumes are reported and discussed in terms of intrinsic and solvational contributions. Rate laws and pressure effects on reactivity are reported for the reaction of peroxodisulphate with pentacyanoferrates(II) containing N-alkylpyrazinium ligands.